This investigation seeks to achieve two main goals: (1) to examine the direct and indirect impact of drug use, as well as other socioeconomic, biomedical, cognitive, emotional, and behavioral factors nested within the structure of the Health Belief Model, on adherence to protease inhibitors (PIH) among HIV seropositive (HIV+) men who have sex with men (MSM) in New York City (NYC); and (2) to explore the consequences of PIH use on HIV transmission sexual risk behaviors in order to understand their role in the continuing epidemic. Our ultimate purpose is to gather information necessary to assist community-based organizations design and implement effective interventions to increase adherence to medication and decrease HIV transmission behaviors among drug using and abusing populations. This research will be undertaken by behavioral research psychologists at the Center for HIV/AIDS Educational Studies and Training (CHEST) at New Jersey City University (NJCU). In addition, researchers from the Columbia University HIV Center, University of California-San Francisco, and St. Lukes/Roosevelt AIDS Center will serve as consultants to the project. The study aims to recruit and then longitudinally follow a sample of 300 HIV+ MSM, stratified based on drug use (100 non drug users, 100 drug-users, and 100 drug abusers) for a 12 month period using both qualitative and quantitative methodologies, as well as electronic, self-report, and biological measures of adherence. Participants will be recruited through active and passive recruitment strategies, targeting AIDS Service Organizations (ASOs), Mainstream Gay Venues (MGVs) such as bars, bookstores, and street corners, and Public Sex Environments (PSEs), in order to obtain a diverse sample of HIV+ MSM in NYC. Generalized linear, Markov regression, and structural equation modeling will be used to achieve the study's goals.